[16.0] web_widget_x2many_2d_matrix: cells with no data error

[jok-adhoc]

Module

web_widget_x2many_2d_matrix

Describe the bug

In 15.0, if there wasn't any data related for a row/column set, the matrix would fill it with a blank space. Now, In 16.0, it raise an owl error.

To Reproduce

Steps to reproduce the behavior:

1. Create matrix.
2. Select a field and axis so that it is a cell that could not match any value while others with the same row or column could (In order to have the axis visible)

Expected behavior It should generate a blank space

Additional context It used to be like this image in 15.0